I've been messing about with my 4770 and have got some decent results:-
It's a VTX3D 4770 with a modified Accelero S1, 120mm Adda fan and Zalman ramsinks, overvolted to 1.2 using MSI Afterburner.
The interesting thing I've found is that the ram doesn't respond to overvolting, it sits at 1200 quite happily on stock voltages. The gpu on the other hand will only hit 840 on stock voltage, 950 on 1.1v and 981 on 1.2v.
Temperatures are really good too, the gpu didn't exceed 50C at any time during furmark and it idles at around 30C (and about 27C on stock volts).